1. Field of the Invention
The present invention relates to a variable stroke engine including: a connecting rod connected at one end to a piston through a piston pin; a subsidiary arm turnably connected at one end to the other end of the connecting rod and connected to a crankshaft through a crankpin; and a control rod connected at one end to the subsidiary arm at a position displaced from a connection position of the connecting rod; a support position of the other end of the control rod being cable of being displaced in a plane perpendicular to an axis of the crankshaft.
2. Description of the Related Art
Such an engine is conventionally known, for example, from Japanese Patent Application Laid-open No. 9-228858, U.S. Pat. No. 4,517,931 and the like, wherein the stroke of a piston in an expansion stroke is made larger than that in a compression stroke, whereby a larger expansion work is carried out in the same amount of an intake air-fuel mixture to enhance the cycle thermal efficiency.
In the above-described conventionally known engine, the stroke of the piston in the expansion stroke is made larger than that in the compression stroke irrespective of the engine load, thereby enhancing the cycle thermal efficiency. However, when the engine load is low, it is desirable that the operation of the engine is carried out while putting a high value on a reduction in fuel consumption.
The present invention has been accomplished with such circumstance in view, and it is an object of the present invention to provide a variable stroke engine, wherein a reduction in fuel consumption can be achieved irrespective of the level of the engine load, while putting a high value on a reduction in fuel consumption in a state in which the engine load is low.
To achieve the above object, the present invention provides a variable stroke engine including: a connecting rod connected at one end to a piston through a piston pin; a subsidiary arm turnably connected at one end to the other end of the connecting rod and connected to a crankshaft through a crankpin; and a control rod connected at one end to the subsidiary arm at a position displaced from a connection position of the connecting rod; a support position of the other end of the control rod being cable of being displaced in a plane perpendicular to an axis of the crankshaft, wherein the engine further includes a switchover means capable of switching over: a state in which a high expansion ratio is provided such that the stroke of the piston in an expansion stroke is larger than that in a compression stroke when an engine load is high; and a state in which a constant compression ratio is provided when the engine load is low.
With such arrangement of the invention, when the engine load is high, the high expansion ratio is provided, and when the engine load is low, the constant compression ratio is provided. Thus, it is possible to provide a reduction in fuel consumption irrespective of the engine load, while enabling the fuel consumption to be further reduced in the state in which the engine load is low.